(1) Field of the Invention
This invention relates to a terminal apparatus used in communication services such as digital satellite broadcasting and digital CATV (Community Antenna Television), and to a method used for the terminal apparatus.
(2) Description of the Prior Art
As the number of channels provided in the satellite broadcasting or CATV has increased greatly, competition among broadcasting companies has been intensified. Broadcasting companies hope that broadcasting systems known as interactive TV broadcasting systems will attract many viewers, and active studies into interactive TV broadcasting systems are under way. The term "interactive" indicates that the user can display desired images by making requests. Suppose, for example, each screen includes a plurality of icons which are related to other pieces of image information which form screens. It is supposed that in the interactive TV broadcasting system, a desired piece of image information is displayed when the operator selects an icon on the interactive screen. The operator feels as if he/she could display what he/she desired. Such an interactive TV broadcasting system is epoch-making in TV broadcasting where one-way broadcasting has long been the norm. There is a possibility that the interactive TV broadcasting system will become a next-generation standard for TV broadcasting system.
Such an interactive TV broadcasting system may be achieved by a method in which each terminal apparatus sends a request for transmitting a desired piece of image information to the broadcasting station, and in response, the broadcasting station transmits the desired piece of image information to the terminal apparatuse. For achieving this, the broadcasting station needs to store a large amount of image information which can be provided to the terminal apparatuses.
It is increasingly difficult to achieve the above system as the number of terminal apparatuses increases. This is because a number of communication lines need to be provided for transferring the transmission requests and image information. Such a construction may also suffer from an overflow in handling the transmission requests in the broadcasting station due to an overflow in the communication lines which are used for transferring the read requests and image information. Viewers may stop using such an interactive TV broadcasting system if it takes very long to display a desired image.